Effective management of a fishery requires an understanding of the reproductive biology of the species. One of the only remaining Katelysia fisheries in South Australia is in Coffin Bay, Eyre Peninsula, and currently there is limited information known about their annual changes in reproductive condition. Over six months, Katelysia individuals were collected from six sites across several fishing grounds in Coffin Bay to identify the age, size, and time when the peak spawning period occurs for the three species. Sexes were assessed microscopically, and reproductive phase determined by dissection to score gonad condition. Ages of Katelysia were measured using cross sections of the shell and counting the growth bands. We identified that there were some idiosyncratic patterns across sites and months around predicted peak spawning times. These results will be useful for predicting when individuals are sexually mature across the commercial fishing grounds. Age at maturity information will also be important for commercial fishers to use less invasive techniques to determine the age of individuals and adjust fishing times around recruitment peaks. Overall, these findings will be important for the advancement of the Coffin Bay fishery to avoid overexploitation and ensure food security for the future.